gsm system survey

GSM System Survey

Produced by:MSC Performance GroupOperations and Engineering DepartmentVodafone Egypt

Contents Chapter 1 : Introduction

Chapter 2 : Basic GSM Network Structure

Chapter 3 : Transmission System

Chapter 4 : Radio Coverage

Chapter 5 : Radio Problems and digital

information

Chapter 6 : Air interface

Chapter 7 : Traffic Cases

Chapter 8 : GSM Services

Questions Questions ??

Banner Advertisement. America 1929

Chapter 1 : Introduction

Chapter Objectives

By the End of this Chapter you will:

Know the History of TelecommunicationsKnow the history of GSM evolutionKnow about different GSM Phases

GSM System Survey

Introduction

History of Wireless Communication

GSM System Survey

Date Place Activity

1921 Chicago 2 MHz Vehicular Mobile Radio system for Police Applications

1930s US Invention of Amplitude Modulation. Half Duplex transmission

1935 US Invention of Frequency Modulation. Improved Audio Quality

1946 St. Louis FCC First Domestic Public Land Mobile service at 150 MHz

1969 Europe Denmark, Finland, Iceland, Norway and Sweden form the first standardization group: Nordic Mobile Telephony (NMT)

1973 Europe NMT specifies standards to allow mobiles phones to be located within or across their networks. Basis for roaming idea

1979 Chicago Advanced Mobile Phone System. First Cellular Analog network

1991 Europe The First Digital Cellular Standard (GSM) is launched

Introduction

GSM System Survey

Date Activity

1982

Nordic Telecom and Netherlands PTT send a proposal to the Conférence Européenne des Postes et Télécommunications (CEPT) to specify a common European mobile telecommunication service.

The European Commission (EC) issues a directive, which requires member states to reserve frequencies in the 900 MHz band for GSM.

1986

Field tests were held in Paris and a GSM permanent nucleus was created and comparative tests of 8 prototypes were performed.

The choice was Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA).

1987

A Combination of TDMA and FDMA selected as the transmission tech. for GSM. September – 13, operators and administrators from 12 areas in the CEPT GSM

advisory group sign the charter GSM (Groupe Spéciale Mobile) MoU "Club" agreement, with a launch date of 1 July 1991.

The original French name was later changed to Global System for Mobile Communications, but the original GSM acronym stuck.

GSM spec drafted. (Digital Transmission, Time Multiplexing of order 8 and slow Hopping)

1988 CEPT began producing GSM specifications for phased implementation. Another five countries signed the MoU

Introduction

History of GSM

Date Activity

1989

The European Telecommunications Standards Institute (ETSI) defined GSM as the internationally accepted digital cellular telephony standard and took over responsibility of GSM specifications.

1990 Phase 1 specifications were frozen to allow manufacturers to develop network

requirements and the first GSM prototype was brought to service.

1991 The GSM 1800 standard was released. An addendum was added to the MoU allowing countries outside CEPT to sign.

1992

Phase 1 specifications were completed. January - First commercial phase 1 GSM network operator is Oy Radiolinja Ab in

Finland December 1992 - 13 networks on air in 7 areas First International roaming agreement was signed between Telecom Finland and

Vodafone in UK.

1993

Australia became the first non-European country to sign the MoU. The MoU now had a total of 70 signatories.

GSM demonstrated for the first time in Africa at Telkom '93 in Cape Town GSM networks were launched in Norway, Austria, Ireland, Hong Kong and Australia. The number of GSM subscribers reached one million. The first commercial DCS 1800 system was launched in the U.K. December 1993 - 32 networks on air in 18 areas

GSM System Survey

Introduction

History of GSM

Date Activity

1996

GSM MoU is formally registered as an Association registered in Switzerland December 1996 120 networks on air in 84 areas 8K SIM launched Pre-Paid GSM SIM Cards launched Option International launches world's first GSM/Fixed-line modem Nov 1996 - Sole Governmental operator in Egypt goes online.

1997 First dual-band GSM 900-1900 phone launched by Bosch

1998

At the beginning of 1998 the MoU has a total of 253 members in over 100 countries and there are over 70 million GSM subscribers worldwide. GSM subscribers account for 31% of the world’s mobile market

Vodacom Introduces Free Voice Mail GSM SIM Cracked in USA 21 May 1998. Egypt privatizes its GSM operator. Iridium Live 11/98 125m GSM 900/1800/1900 users worldwide (12/98) 1 Dec 1998. Click GSM commercial launch.

GSM System Survey

Introduction

History of GSM

Introduction

GSM Coverage worldwide

Chapter 2 : GSM Network Elements

We hear Music .. But we don’t see the musicians ..

Chapter Objectives


Know the role of the Basic nodes that compose the GSM networkKnow how they are interconnected togetherKnow the different Identities used in GSM World

GSM System Survey

Basic GSM Network Structure

BSC

MS

BTS

PTT

Other Switching

Nodes

HLR

Radio Interface

PABXAnother MSC

GW Of another network

GSM System Survey


Basic GSM Nodes

MSC/VLR

AUC

Administers its Base Station Controller(s) BSC(s).

Switches calls to/from mobile subscribers.

Records charging and accounting details.

Provides the gateway functionality to other networks.

GSM System Survey


The Mobile Services Switching Center (MSC)

Basic subscriber categories.

Supplementary services.

Current location(MSC address).

Allowed/barred services.

Authentication data.

GSM System Survey


The Home Location Register (HLR)

Controls the routing of mobile terminated calls and SMS.

Stores for each mobile subscriber:

Authentication Center

Triplet

RAND SRES Kc

Home Location Register

Triplet

RAND SRES Kc

Visitor Location Register

RAND SRES Kc

GSM System Survey


Triplets

Ciphering Algorithm

A8

Ciphering Algorithm

A8

IMSIKi

Authentication Algorithm

A3

Authentication Algorithm

A3

Random Number

Generator

Random Number

Generator

SRES

RAND

Kc

SRESSRES

RANDRAND

KcKc

RANDKi

RANDKi

GSM System Survey


Producing Triplets

Visitor Location Register

Rand SRES AUC Kc

SRES AUC SRES MS

Barred

Base Station Subsystem

Kc

SIM Card

A8

SRES MS

= Access

Kc

SRES MSRand

Rand

A3 KiRand

GSM System Survey


The Authentication Procedure

GSM System Survey


The Ciphering Procedure

Base Transceiver StationDecryptionAlgorithm

Encryption Algorithm

From the BSCTo the BSC

Mobile Station

TDMA Frame Number

DATA

En

cryp

ted

D

AT

A

DATA

En

cryp

ted

D

AT

A

Encryption Algorithm

DecryptionAlgorithm

Kc

TDMA Frame Number

DATA DATA

Kc

Air Interface

It stores a copy of the HLR Profile for all currently registered mobile

subscribers who are covered by cells belonging to the MSC coverage

area. The VLR is always integrated with the MSC. The VLR stores the Location area of the MS (which is not stored in the

HLR).

GSM System Survey


The Visitor Location Register (VLR)

Manages the Radio Communication with the mobile station over the air interface.

Controls the handover of calls in progress Between BTSs Supervises the transmission network and the operation of each BTS

GSM System Survey


The Base Station Controller (BSC)

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The Base Transceiver Station (BTS)

Consists of the radio transmitters, receivers and the antenna system required to provide the coverage area for one cell.

Converts the GSM radio signals into a format that can be recognized by the BSC.

Records and passes to the BSC the Signal strength measurements.

Performs the network end of the ciphering/encryption process.

The SIM Card contains:

A processor and memory.

that stores: - The international mobile subscriber Identity IMSI

- The Authentication and ciphering keys.

The Mobile Equipment is said to be a Mobile Station if the Subscriber Identity Module ( SIM Card ) is added to it

+GSM System Survey


The Mobile Station (MS)

GSM System Survey


CC : Country CodeNDC : Network Destination CodeSN : Subscriber Number

VodaFone Egypt MSISDN

20

CC

10

NDC

1100477

SN

Mobile Station ISDN Number (MSISDN)

VodaFone UK MSISDN

44

CC

385

NDC

196099

SN

GSM Identities

GSM System Survey


International Mobile Subscriber Identity (IMSI)

MCC : Mobile Country CodeMNC : Mobile Network CodeMSIN : Mobile Station Identification Number

Vodafone UK IMSI

234

MCC

15

MNC

1234567890

MSIN

Vodafone Egypt IMSI

602

MCC

02

MNC

1234567890

MSIN

GSM Identities

GSM System Survey


International Mobile Equipment Identity (IMEI)

IMEI

6 Digits

TAC

2 Digits

FAC

6 Digits

SN

TAC: Type Approval Code, The first two digits are the code for the country approvalSN: Serial Number

Final Assembly Codes (FAC)

01,02 AEG07,40 Motorola10,20 Nokia30 Ericsson40,41,44 Siemens47 Optional International50 Bosch51 Sony51 Siemens51 Ericsson60 Alcatel70 Sagem75 Dancall80 Philips85 Panasonic

GSM Identities

Temporary Mobile Subscriber Identity Number (TMSI)

The TMSI can be allocated to the mobile subscriber in order to be used instead of his IMSI during all radio communications. The purpose is to keep subscriber information confidential on the air interface.

The TMSI is relevant on the local MSC/VLR level only and is changed at certain events or time intervals. Each local operator can define its own TMSI structure.


GSM Identities

GSM System Survey

Mobile Station Roaming Number (MSRN)

When a mobile terminating call is to be set-up, the HLR of the called subscriber requests the MSC/VLR to allocate an MSRN to the called subscriber.

This MSRN is returned via the HLR to the GMSC.

The GMSC routes the call to the MSC/VLR exchange where the called subscriber is currently registered.

The routing is done using the MSRN. When the routing is completed, the MSRN is released.

The interrogation call routing function (request for MSRN) is part of the MAP.

All data exchanged between GMSC-HLR-MSC/VLR for the purpose of interrogation is sent over S7 signaling.

The MSRN is built up like an MSISDN.


GSM Identities

GSM System Survey

GSM System Survey


SSSS

D T I

BTSBTSO S S

ISDN

PLMN

PSTN

ISDNISDN

PLMNPLMN

PSTN M I N

S C

B G W

H L R

AUC

SMSC-GMSCSMS-IWMSC

E I R

GWMSCGWMSC

MSC/VLRMSC/VLR

MSMS

Air I/fGPRS

SGSN

BSC/TRCBSC/TRC

BSSBSS

GSM Network Structure

GSM System Survey


Vodafone Egypt Network Structure

HORUS OSIRIS ISIS OPET SETH

HATHOR AMUN THOTH NEFTIS NUN

MINA NEITHBTAH ABIS SEKHMET


GSM System Survey

Chapter 3 : Transmission System

We mean by a transmission system, how the nodes are interconnected

Chapter Objectives


Know How do we use TE infrastructure in connecting our NodesKnow the basic role of the DXX

GSM System Survey

Transmission System

BSC

MS

BTS

PTT

Another Switching

Node

HLR

MSC/VLR

Radio Interface

PABX Another MSC

GW Of another network

Transmission System

Review the System

GSM System Survey

Digital Communication offers better noise performance

GSM System Survey

Radio Coverage

Digital Versus Analog Transmission

Transmission SystemTE Adjacent Switch

TE Fiber

Backbone

TE Fiber Backbone

Misrfone Switch

BSC

Digital DistributionFrame

DDF

Synchronous Transport Module

155 Mb/sec

STM

2 Mb/sec

Ramsis PTT

2 Mb/sec

RBLT

SDH

AswanPTT

Suez PTT

AlexPTT

DDFADM

Add / DropMultiplexer

ADMB/B

Con

.

GSM System Survey

Misrfone Switch

DDF

2 Mb/secSDH

DDF

TE RemotePTT

0 1 2 .. .. .. 29 30 31

Ramsis PTT

BSC

RBLT

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Transmission System

Transmission system

Misrfone Switch

BSC

Ramsis PTTRBLT

DDF

0 1 2 .. .. .. 13 14 15

0 1 2 .. .. .. 13 14 15

DDF

16 17 .. .. .. 28 29 31

TE RemotePTT

GSM System Survey

Transmission System

Insufficient use of resources

Ramsis PTT

HUB

RDXX

DDFDDF

BSC

RBLT

LDXX

TE RemotePTT

Misrfone Switch

GSM System Survey

Transmission System

Introducing DXX


GSM System Survey

Chapter 4 : Radio Coverage

A visible pattern of sound waves

Chapter Objectives


Know The Geometrical Theoretical shape of the cellsKnow the frequency band allocated for GSMKnow what is meant by frequency ReuseKnow when to use different cluster sizes

GSM System Survey

Radio Coverage

Dead Spots

Problem of omni directional antennas

GSM System Survey

Radio Coverage

Cell Geometry

R R

To solve the dead spot problem

• The number of cells required to cover a given area.

• The cell transceiver power.

Tradeoffs R

GSM System Survey

Radio Coverage

Cell Geometrical Shape

Omni-Directional AntennaSectorial Antenna

GSM System Survey

Radio Coverage

Transceiver Antenna

The cells will take the form of overlapping circles.

Due to the obstacles in the coverage area the actual shape of the cells would be Random.

Sectorial Antenna

GSM System Survey

Radio Coverage

Sectorial Antenna

Umbrella Cell

Overlaid & Underlaid CellsNormal Cell Normal Cell

GSM System Survey

Radio Coverage

Cell ClassificationMacrocell

Microcell

Slow moving subscribers

Fast moving subscribers

Picocell

In buildingcoverage

To provide coverage for a large service area of a mobile network we have two Options:

(A) Install one transceiver with high radio power at the center of the service area

Drawbacks

• The mobile equipments used in this network should have high output power in order to be able to transmit signals across the coverage area.

• The usage of the radio resources would be limited.

(B) Divide the service area into smaller areas (cells)

Advantages

• Each cell as well as the mobile handsets will have relatively small power transceivers.

• The frequency spectrum might be “reused” in two far separated cells. This yields:

Unlimited capacity of the system.

Good interference characteristics

GSM System Survey

Radio Coverage

GSM Coverage Plan

GSM System Survey

Radio Coverage

Spectrum Allocation (GSM 900)

GSM 900 Frequency Allocation

F (MHz)915890

Uplink1 2 3 4 121 122 123 124

F (MHz)

Downlink

960935

1 2 3 4 121 122 123 124

890.2

890.4

890.6

935.2

935.4

935.6

200 KHz

1

1

121

121

Downlink 935 – 960 MHz

Uplink 890 – 915 MHz

ARFCN Absolute Radio Frequency Channel Number

GSM 1800 Frequency Allocation

F (MHz)17851710

Uplink1 2 3 4 371 372 373 374

F (MHz)

Downlink

18801805

1 2 3 4 371 372 373 374

1710.2

1710.4

1710.6

1805.2

1805.4

1805.6

200 KHz

Downlink 1805 – 1880 MHz

Uplink 1710 – 1785 MHz

GSM System Survey

Radio Coverage

Spectrum Allocation (GSM 1800)

890 915

935 960

GSM 900With 124 ARFCN

25 MHz

45

MH

z

Uplink

Downlink

1710 1785

1805 1880

GSM 1800With 374 ARFCN

75 MHz

95

MH

z

Uplink

Downlink

GSM System Survey

Radio Coverage

Comparison

Total no of channels (frequencies) = 124

Every channel can be shared between a maximum of 8 subscribers.

Maximum no of simultaneous calls = 8 X 124 = 992 !!

Why do we need frequency reuse?

The frequency reuse is performed by dividing the whole available frequencies between a group of neighboring cells which is called frequency reuse pattern or a “Cluster”, and then repeat this cluster over the whole network on 2 conditions:

The group of frequencies allocated to a given cell must not be used in the adjacent cells.

Enough distance between the cells where the same group of frequencies are reused.

GSM System Survey

Radio Coverage

Frequency Reuse

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

3/9 cluster in which the available frequencies are divided into 9 groups and distributed between 3 sites

A3

A2

A1

B3

B2

B1

C3

C2

C1

A3

A2

A1

B3

B2

B1

C3

C2

C1

GSM System Survey

Radio Coverage

3/9 Cluster

4 / 12 Cluster

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

4/12 cluster in which the available frequencies are divided into 12 groups and distributed between 4 sites

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

A3

A2

A1

B3

B2

B1

C3

C2

C1

D3

D2

D1

GSM System Survey

Radio Coverage

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

A3

A2

A1

C3

C2

C1

D3

D2

D1

B3

B2

B1

E3

E2

E1

F3

F2

F1

G3

G2

G1

7 / 21 cluster in which the available frequencies are divided into 21 groups and distributed between 7 sites

GSM System Survey

Radio Coverage

7 / 21 Cluster

Carrier to interference ratio

It’s the difference in power level between the carrier in a given cell and the same carrier received from the nearest cell that reusesthe same frequency.

Number of frequencies per site

Traffic ChannelsC/I Ratio

3/9 High High Low

4/12 Medium Medium Medium

7/21 Low Low High

GSM System Survey

Radio Coverage

Which Cluster Size to use?


GSM System Survey

Chapter 5 : Radio problems & Digital Information

Chapter Objectives


Know the Fading Problem and how it is SolvedKnow the Time Dispersion Problem and how it is SolvedKnow the Time Delay Problem and how it is SolvedKnow how the Digital information is coded

The reason for shadowing is the presence of obstacles like large hills or buildings in the path between the site and the mobile. The signal strength received fluctuates around a mean value while changing the mobile position resulting in undesirable beats in the speech signal.

2. Rayleigh Fading (Multi-path Fading)

The received signal is coming from different paths due to a series of reflection on many obstacles. The difference in paths leads to a difference in paths of the received components.

1. Shadowing (Normal fading):

GSM System Survey

Radio Problems and digital information

Fading Problems

GSM System Survey

Fading Problems


GSM System Survey

Fading Problems Solutions

time

Fading Margin

ReceiverSensitivity

db

1. Increase the fading Margin


GSM System Survey

Fading Problems Solutions

The cell transceiver will use two receiving antennas instead of one. They will be separated by a distance of about 5 meters, and they will receive radio signals independently, so they will be affected differently by the fading dips and the better signal received will then be selected.

3. Frequency hopping (frequency Diversity)

2. Antenna diversity (Space Diversity)

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7t

F

f3

f2

f1


Frame Rate = 270.8 Kb/s

One BIT Duration = 3.7 sec

Bit stream is moving with the velocity of light which equals 3 x 10 5 Km/sec

Then, when bit 2 is transmitted, bit one will cut a distance = 3.7 x 10 -6 x 3 x 10 5 = 1.1 km

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

270.8 Kb/s

GSM System Survey

Time dispersion problem

270.8 Kb/s 270.8 Kb/s


GSM System Survey

Time dispersion problem

Direct ray 1.1Km

1.1Km1.1K

m

There would be an interference between the a bit in the reflected ray and 1 bit later in the direct way .


The C/R ratio is defined as the difference in signal strength between the signal received from the RBS and the strongest reflected signal .

C/R Relative position to the BTSResult

Planner should choose the proper position of the site to make the C/R maximum everywhere in the coverage area of the site.

GSM System Survey

Time dispersion problem Solution

1. Increase the Carrier to reflection ratio


GSM System Survey

Time dispersion problem Solution

2. Use Viterbi Equalizer

Choose xxx so that the difference between T

and T* is the minimum

Probable received

bit pattern

Received Bits

Correlator

Channel Model

Data T* Data

xxx T xxx

Compare

VITERBI


If a mobile subscriber is located far from the site, then its transmitted bursts will arrive at the cell transceiver with a significant delay that may lead to overlapping with the bursts sent on the next time slot.

Solution to time delay problem

The site will send a “Timing Advance” value to the mobile station that is moving away, telling it to send its bursts with a certain amount of time ahead of the synchronization time. The timing advance has values from 0 to 63 depending on how far the mobiles located. The size of a cell is limited by this parameter to a maximum radius of 35 Km.

GSM System Survey

Time Delay problem


GSM System Survey

GSM Transmission Process

Segmentation

Speech Coding

Channel Coding

Interleaving

Ciphering/Encryption

A/D Conversion

Burst Formatting

Modulation and

Transmission


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Analog to Digital Conversion

GSM System Survey

Analog to digital conversion takes place in 3 steps:

1. Sampling2. Quantization3. Coding

1. Sampling

Telecommunication systems use Sampling rate = 8 Kbit/s


2. Quantization

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission


GSM System Survey

Within common telephony, 256 levels are used while in GSM 8192 levels are used.


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission


GSM System Survey

Coding involves converting the quantized values into binary.Every value is represented by a binary code of 13 bits (2 13 = 8192).

1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10

The output rate of the A/D Conversion process is:8000 Samples/Sec x 13 bits/Sample = 104 Kb/sIf one frequency will be used for 8 calls, then the bit rate will be 8 x 104 kb/s = 832 kb/s this will not fit in the 200 KHz channel allocated for one frequency. Coding should be used to reduce the rate.

3. Coding


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

GSM System Survey

1 2 3 4 5 6 7 8 9 10 11 12 13 0 1 2 3 4 5 6 7 8 9 10

160 sample in 20 ms = 1 Segment

1 2 3 4 . . . . . . . . . . . . . . . 160


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

GSM Speech Coding

GSM System Survey

Instead of using 13 bits per sample as in A/D conversion, GSM speech coding uses 260 bits to encode one segment.

This calculates as 260 bits / 20 ms = 13 kb/s. This provides a speech quality which is acceptable for mobile telephony and comparable with wire line PSTN phones.

Many types of speech coders are available. Some offer better speech quality, at the expense of a higher bit rate (waveform coders). Others use lower bit rates, at the expense of lower speech quality (vocoders). The hybrid coder used by GSM provides good speech quality with a low bit rate, at the expense of speech coder complexity.


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Channel Coding

GSM System Survey

speech coding does not consider the problems which may be encountered on the radio transmission path. The next stages in the transmission process, channel coding and interleaving, help to overcome these problems.

Inp

ut

is 2

60 b

its

rep

rese

nti

ng

1 s

egm

ent


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Interleaving

GSM System Survey

1. First Level Interleaving

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

17 18 19 20 21 22 23 24

25 26 27 28 .. .. .. ..

.. .. .. .. .. .. .. ..

.. .. .. .. .. .. .. ..

.. .. .. .. .. .. .. ..

.. .. .. .. .. .. .. ..

429 430 431 432

433 434 435 436 437 438 439 440

441 442 443 444 445 446 447 448

449 450 451 452 453 454 455 456

57 Bits

8 Groups


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Interleaving

GSM System Survey

2. Second Level Interleaving

1 A T 5 D

2 A T 6 D

3 A T 7 D

4 A T 8 D

1 B T 5 A

2 B T 6 A

3 B T 7 A

4 B T 8 A

1 C T 5 B

2 C T 6 B

3 C T 7 B

4 C T 8 B

1 D T 5 C

2 D T 6 C

3 D T 7 C

4 D T 8 C

12345678

20 ms Block A12345678

20 ms Block A

12345678

20 ms Block D12345678

20 ms Block D

12345678

20 ms Block c12345678

20 ms Block c

12345678

20 ms Block B12345678

20 ms Block B


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Ciphering and Encryption

GSM System Survey

The purpose of ciphering is to encode the burst so that it cannot be interpreted by any other device than the intended receiver.The ciphering algorithm in GSM is called the A5 algorithm. It does not add bits to the burst, meaning that the input and outputto the ciphering process is the same as the input: 456 bits per 20 ms.


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Burst Formatting

GSM System Survey

Every transmission from an MS/BTS must include some extra information such as the training sequence. The process of burst formatting is to add these bits (along with some others such as tail bits) to the basic speech/data being sent.

In GSM, the input to burst formatting is the 456 bits received from ciphering. Burst formatting adds a total of 136 bits per block of 20 ms, bringing the overall total to 592.

Now, the 592 bits will be sent on 4 bursts, each containing 2 x 57 bits + 136 / 4 = 148 bits.

However, each time slot on a TDMA frame is 0.577 ms long. This provides enough time for 156.25 bits to be transmitted (each bit takes 3.7 us), The rest of the space, 8.25 bit times, is empty and is called the Guard Period (GP). This time is used to enable the MS/BTS “ramp up” and “ramp down”.


To ramp up means to get power fromthe battery/power supply for transmission.

Ramping down is performed after each transmission to ensure that the MS is not transmitting during time slots allocated to other MSs.

The output of burst formatting is a burst of 156.25 bits or 625 bits per 20 ms. When it is considered that there are 8 subscriber per TDMA frame, the overall bit rate for GSM can be calculated to be 270.9 kbits/s.

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Burst Formatting

GSM System Survey

Guard Period

Tail Bits

Encrypted BitsTraining

SequenceEncrypted Bits

Tail Bits

8.253571261573

TDMA Frame

76543210

156.25 bits in 577 u Sec


Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Segmentation

Speech Coding

Channel Coding

Interleaving


A/D Conversion

Burst Formatting

Modulation and

Transmission

Modulation and Transmission

GSM System Survey


Chapter 6 : Air Interface

Chapter Objectives


Know How the Physical and Logical Channels are classifiedKnow the different types of Traffic ChannelsKnow the different types of Control Channels Know the Structure of each Control ChannelKnow how control and traffic data is Mapped in the air interfaceKnow the terminology of different TDMA Frames

Air Interface

Physical Channels

GSM System Survey

Time

GSM band is divided into 124 RF channels, and each channel is divided into 8 time slots using TDMA. These time slots are called “physical channels”.

CH 1 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

CH 2 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

CH 3 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

CH 124 0 1 2 3 4 5 6 7 0 1 2 3 4 5

Air Interface

Logical Channels

GSM System Survey

Logical Channels

A physical channel may be occupied by a traffic channel or a control channel, both of them are classified as “logical channels”.

Traffic Channels

Half Rate Full Rate

Control Channels

SCH

BCCH

FCCHPCH

RACH

ACGCH

SDCCH

SACCH

FACCH

CBCCH

BroadcastCommon Dedicated

Air Interface

Traffic Channels

GSM System Survey

Carries either encoded speech or user data up and down link between a single mobile and a single BTS.

Full Rate = 13 Kbit/S

Half Rate = 6.5 Kbit/S

Enhanced Full Rate = 15.1 Kbit/S

Random Access CHannel (RACH)

Access Grant CHannel (AGCH)

It’s used to page (search) for a specific mobile

To or from a certain BTS to a single mobile

Request allocation of SDCCH

Allocate SDCCH to the mobile station.

Air Interface

Common Control Channels

GSM System Survey

Paging CHannel (PCH)

Frequency Correction Control CHannel (FCCH)

From Single BTS to all the mobiles in the area

Carries information for frequency correction of the mobile

Synchronization CHannel (SCH)

Carries 2 important pieces of information

• TDMA frame number (max = 2715684 )

• Base station identity Code (BSIC)

Broadcast Control CHannel (BCCH)

Carries Cell specific data

Air Interface

GSM System Survey

Broadcast Channels

Air Interface

GSM System Survey

Dedicated Control Channels

Standalone Dedicated Control CHannel (SDCCH)

Carries system signaling during:

A call setup before allocating a TCH.

Registration & Authentication.

Transmission of SMS in idle mode.

MS paging Response.

Cell Broadcast Control CHannel (CBCCH)

MS must be setup to receive this channel.

It displays general information.

It uses one of the SDCCH channels

Air Interface

GSM System Survey

Normal Burst Structure

It carries information of all logical channels except RACH, SCH and FCCH

Tail Bits

Encrypted Bits

Training Sequence

Encrypted Bits

Tail Bits

Guard Period

3 57 1 26 1 57 3 8.25

0 1 2 3 4 5 6 7

TDMA Frame


The tail bits help the equalizer to determine the start and stop points of the transmitted bits. They are three bits at the beginning and at the end of the burst and they are always zeros

The subscriber speech or data is encrypted into 57 bit blocks. Each burst will contain two 57 bits blocks from two different speech segments.

One bit “stealing flag” will be added to each block to indicate whether the burst is stolen for the FACCH signaling or used as a normal traffic channel

The training sequence is inserted in the middle of the burst to help the Viterbi equalizer to create the channel model

The guard period of 8.25 bits length, which is equivalent to about 30 s, is left at the end of each burst, to prevent overlapping between consecutive bursts and to facilitate burst synchronization

Tail Bits Fixed Bits

Tail Bits

Guard Period

3 142 3 8.25

This is the one used by the channel (FCH) for frequency correction of the mobile. It consists of a long sequence of bits called the fixed bits which are all equal to zeros, leading to a constant frequency output from the GMSK modulator

0 1 2 3 4 5 6 7

TDMA Frame


Air Interface

GSM System Survey

Frequency Correction Burst Structure

0 1 2 3 4 5 6 7

TDMA Frame


Air Interface

GSM System Survey

Synchronization Burst Structure

Tail Bits

Encrypted Bits

Synchronization Sequence

Encrypted Bits

Tail Bits

Guard Period

3 39 64 39 3 8.25

The SCH burst consists of a long synchronization sequence along with the important information being encrypted and divided into two blocks. The TDMA frame number is sent on the SCH channel, which carries also the Base station Identity code (BSIC). The TDMA frame number is used by the mobile to determine which control channels will be transmitted on that frame. It is used also as one of the input parameters to the algorithm that calculates the ciphering key Kc, which is in turn used for encryption of subscriber information transmitted on the air interface

Tail Bits

Synchronization Sequence

Encrypted Bits

Tail Bits Guard Period

8 41 36 3 68.25

The Access Burst is used by the RACH channel. The mobile sends this burst when it does not know the distance to its serving BTS, which is the case when the mobile is switched on or after it makes a handover to a new cell. So this burst must be shorter in order to prevent it from overlapping with the burst on the next time slot

Air Interface

GSM System Survey

Access Burst Structure

0 1 2 3 4 5 6 7

TDMA Frame


Air Interface

GSM System Survey

Dummy Burst Structure

0 1 2 3 4 5 6 7

TDMA Frame


Tail Bits Encrypted Bits

Training Sequence

Encrypted BitsTail Bits

Guard Period

3 58 26 58 3 8.25

The dummy burst is sent from the BTS when there is nothing else to be sent. It carries no information and it has the same structure of a normal burst with the encrypted bits replaced by a known bit pattern to the mobile

CBBBBSF

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

F S F S F S F S F S I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

B C C C C C C C C C

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7

Mapping of the 51 burst consumes 51 TDMA frame

51 TDMA Frame = 1 Multi-frame

GSM System Survey

Air Interface

Mapping of Logical Channels onto timeslot 0 (Downlink)

RRRRRRR

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Time slot 0 in the uplink direction is reserved for the RACH channel which is used by the mobiles to make random access request to the system

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7


GSM System Survey

Air Interface

Mapping of Logical Channels onto timeslot 0 (Uplink)

GSM System Survey

Air Interface

Mapping of Logical Channels onto timeslot 1 (Downlink)

D1D1D1D0D0D0D0

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

I I I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 A3

I I I

52 102

D0 D1 D2 D3 D4 D5 D6 D7 A4 A5 A6 A7


0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

A6A6A6A5A5A5A5

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

I I I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

A5 A6 A7 D0 D1 D2 D3 D4 D5 D6 D7 A0

I I I

52 102

A1 A2 A3 D0 D1 D2 D3 D4 D5 D6 D7 A4

GSM System Survey

Air Interface

Mapping of Logical Channels onto timeslot 1 (Uplink)


0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

TTTTTTT

2 4 6 8 10 12 14 16 18 20 22 24 261 3 5 7 9 11 13 15 17 19 21 23 25

A (SACCH) This contains the control signaling, an example of this is in order to change output power.

26 TDMA Frames =

1 Traffic Multi-frame

GSM System Survey

Air Interface

Mapping of Logical Channels onto timeslots 2 / 7


0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

T T T T T T T T T T T T A T T T T T T T T T T T T I

Frame F D T R A TS D T R A TB D T R A TB D T R A TB D T R A TB D T R A TC D T R A TC D T R A TC D T R A TC D T R A TF D T R A TS D T R A T

Frame C D A I A I A I R I A I A I A IC D T R I TC D T R I TC D T R D TC D T R D TC D T R D TC D T R D TC D T R D TF D T R D TS D T R D TC D T R D TC D T R D TC D T R D T

Frame C D I A I A I A R D I A I A I AC D T R D TC D T R D TC D T R D TC D T R D TF D T R D TS D T R D TC A T R D TC A T R D TC A T R D TC A T R D TC A T R D TC A T R D T

Frame C A A I A I A I R D A I A I A IC A T R D TF A T R D TS A T R D TC A T R D TC A T R D TC A T R D TC A T R D TC A T R D TC A T R A TC I T R A TC I T R A T

Frame I I T R A T

Downlink Uplink

51 T

DM

A F

ram

es =

1 B

CC

H M

ult

i-fr

ame

GSM System Survey

Air Interface

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

F S F S F S F S F S I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

B C C C C C C C C C

T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T T T T T T T

I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T T T T T T

T I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T T T T T

T T I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T T T T

T T T I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T T T

T T T T I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T T

T T T T T I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T T

T T T T T T I T T T T T T T T T T T T A T T T T T T T T T T T T I T T T T T T T T T T T T A T T T T T

The Sliding Multi-frame

Air Interface

GSM System Survey

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7


Offset

GSM System Survey

Air Interface

Traffic Channel Offset

GSM System Survey

3 57 1 26 1 57 3 8.25

0 1 2 3 4 5 6 7

156.25 bits in 577 m Sec

Normal burst

1 2 e.g. TCH 26 1 2 e.g. BCCH 51

1 e.g. BCCH 26

1 2 e.g. TCH 51

1 2 e.g. BCCH 2048

1 Hyper frame = 2048 Super frames = 2,715,648 TDMA Frames = 3hrs 28 min and 53.76 s

Hyper Frame

Structure

of TDMA Frames

12

1

2

2

1 Super frame = 51 TCH Multi frames

1 Super frame = 26 BCCH Multi frames

1 BCCH Multi frame = 51 TDMA Frames1 TCH Multi frame = 26 TDMA Frames

Air Interface

Scan RF Channel and measure signal Strength for 3 – 5 sec

Tune to the RF channel with the highest received average signal strength

Determine if it is a BCCH carrier by searching for frequency correction bursts

Is it a BCCH carrier?

The MS shall attempt to synchronize to this carrier and read BCCH info

Does the carrier belong to the

wanted PLMN

Is the cell Barred for access ?

Is C1>=0?

Camp on this cell

No

No

No

Yes

Yes

No

Yes

Yes

Measurement in idle mode

C1 ( Path Loss Criterion Parameter) is a parameter used to make sure that the MS camps on the cell with the highest probability of successful communication on the uplink and downlink

GSM System Survey

Air Interface

Tune to the RF Channel with the highest signal strength not already used

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7


0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7


Offset

The mobile is informed on the SACCH channel which BCCH frequencies to be measured.The mobile will try to measure the signal strength of these carriers one by one during the time between transmission and reception of the allocated traffic channel: the mobile transmits, measures and then receives, and so on.To make sure that the measured carriers do not belong to co-channel cells, the mobile will have to check the identity of the adjacent cells by reading the BSIC value sent on the SCH of each cell. This will take place during the idle frame number 26.The signal strength of the serving cell is measured during reception of the allocated traffic channel. Then the mobile will make a list of the strongest six carriers and their BSIC values along with the signal strength of its cell, and reports this list to the BSC via the uplink SACCH channel which is repeated once every 26 frames.

Measurement in active mode

GSM System Survey

Air Interface

Chapter 7 : Traffic Cases

Communicate Anywhere

Chapter Objectives


Know How the Mobile Terminating call is doneKnow how the PLMN Coverage area is divided ( MSC Coverage Areas & Location Areas )Know the different types of Location UpdatesKnow the different types of Handover Procedures Know How the Mobile Originating call is doneKnow the different Traffic Cases a Roamer can have

GSM System Survey

Traffic Cases

Why do we need to update our location data ?

Actually, the location update process is invited in aim to exactly identify your location within the network so that any incoming call goes directly to the called subscriber.

To fulfill this aim, one can say that we may update the system with the cell ID each time the subscriber changes his serving cell.

The MSC/VLR will now know the exact cell you are roaming in.This will result in a huge amount of location update messages.

An extreme is never to make a location update and to be paged in all the network. This will cause huge amount of paging messages.

Do you have a compromising solution ?

GSM System Survey

Location Update

Traffic Cases

Location area is a part of the MSC/VLR coverage area. Each group of adjacent cells is assigned a universal unique location area identity.

The mobile subscriber is only required to update the network with its new location every time it changes its Location Area.

Introducing the concept of Location area enables us to make an approximate estimation of your location.

GSM System Survey

Traffic Cases

Location Area

LA 1

LA 2

MSC

LA 3

LA4

GSM System Survey

Traffic Cases

MSC Coverage Area

GSM System Survey

Traffic Cases

Location Area Identity (LAI)

MCC : Mobile Country CodeMNC : Mobile Network CodeLAC : Location Area Code

Vodafone Egypt LAI

602

MCC

02

MNC

1607

LAC

GSM System Survey

Traffic Cases

Cell Global Identity (CGI)

MCC : Mobile Country CodeMNC : Mobile Network CodeLAC : Location Area CodeCID : Cell ID

Vodafone Egypt CGI

602

MCC

02

MNC

1607

LAC

781

CID

1. Normal Location update within same MSC/VLR service area

2. Normal Location update between 2 different MSC/VLR service areas

3. IMSI attach/detach

4. Periodic Location Update

GSM System Survey

Traffic Cases

Types of Location Update

GSM System Survey

Traffic Cases

Normal Location within the same MSC/VLR Service area

BSC

1. The Mobile sends an allocation request message to the BTS

2. The BTS responds with the allocation message

3. The mobile sends a location update request message with its IMSI to the MSC/VLR

4

4. The MSC/VLR updates the location information and sends a Location Update confirmation message

MSC/VLR

UpdatesLA Record

GSM System Survey

Traffic Cases

Old MSC/VLR New MSC/VLR

NEW BSCOld BSC

LA 1

LA 2

1. The mobile sends a location update request to the MSC.

2. The new MSC/VLR receives the IMSI and conclude the MGT.

IMSI to MGTtranslation

3. The MSC/VLR sends a subscriber information request with the IMSI to the proper HLR

4. The HLR stores the address of the new MSC/VLR

VLR Address=

Old MSC

VLR Address=

New MSC

5. The HLR sends the data to the new MSC/VLR and it is kept there

6. The HLR sends a location cancellation message to the old MSC/VLR to remove the data

HLR

7. The new MSC/VLR sends a location updating confirmation message to the mobile

Normal Location Update between 2 different MSC/VLR service areas

GSM System Survey

Traffic Cases

1. At power off, the MS asks for a signaling channel.

2. The MS uses this signaling channel to send the IMSI detach message to the MSC/VLR.

3. In the VLR, an IMSI detach flag is set for the subscriber. This is used to reject incoming calls to the MS.

IMSI Detach

IMSI attach is a complement to the IMSI detach procedure. It is used by the mobile subscriber to inform the network that it has re-entered an active state and is still in the same location area. If the MS changes location area while being switched off, a normal location update takes place.

1. The MS requests a signaling channel.

2. The MSC/VLR receives the IMSI attach message from the MS.

3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready for normal call handling.

4. The VLR returns an acknowledgment to the MS.

MSC/VLRBSC

1

2 3

4

IMSI Attach

GSM System Survey

Traffic Cases

Periodic location update is a routine task performed by the network if the MS doesn’t make any location update ( any of the previous 4 types) during a predefined period.

If the MS doesn’t respond to this periodic location update, it will be marked as implicitly detached. ( Temporarily out of service )

GSM System Survey

Traffic Cases

Periodic Location Update

Handover is to keep continuity of the call when the subscriber is roaming along the network moving from one cell to another and moving between different nodes in the network.

During call, the MS is continuously measuring transmission quality of neighboring cells and reports this results to the BSC through the BTS.

The BSC, being responsible on supervising the cells, is responsible of handover initiation.

Good neighbor relations between cells is an important factor in keeping the network performance in the accepted level.

GSM System Survey

Traffic Cases

Handover

1. Intra BSC Handover:When the cell to which the call will be handed over belongs to the same BSC of the serving cell.

2. Inter BSC / Intra MSC Handover:When the cell to which the call will be handed over belongs to the different BSCs but to the same serving MSC.

3. Inter MSC When the cell to which the call will be handed over belongs to the different BSC and different MSC.

GSM System Survey

Traffic Cases

Types of Handover

BSC

Serving Cell New Cell

1. The BSC decides from the power measurement reports that the call must be handed over to another cell

2

2. The BSC checks for an vacant TCH in the new cell and orders this cell to activate the TCH

3

3. The BSC orders the serving cell to send a message to the MS telling the informationof new TCH

4. The MS tunes to the new frequency and Sends handover access burst

4

5. The new cell detects the handover burst and sends information about the suitabletiming advance to the MS

5

6. The MS sends a HO complete message to the new cell

6

7. The new cell sends a message to the BSC that the handover is successful

7

8. The BSC orders the old Cell to release the TCH

8

GSM System Survey

Traffic Cases

Intra BSC Handover

GSM System Survey

Traffic Cases

Inter BSC /Intra MSC Handover

Old BSC New BSC

MSC/VLR

Old MSC

GSM System Survey

Traffic Cases

Old BSC

New MSC

Inter MSC Handover

New BSC

Old BSC

New MSC

New BSC

GMSC

PSTN

GSM System Survey

Traffic Cases

Inter MSC Handover

Old MSC

1. The mobile sends a call request along with its IMSI to its serving MSC/VLR which will mark the mobile as busy.

2. Authentication is performed by the MSC to verify the mobile access to the network, and then ciphering is initiated in order to protect the mobile call on the radio path.

3. The mobile sends a call setup message to the MSC with information about the call type, services required and the dialed number.

4. MSC checks the categories of the mobile subscriber to verify that he is authorized to use the required services, and then a link is established between the MSC and BSC.

5. BSC checks the mobile serving BTS for an idle traffic channel and then orders that BTS to seize this channel for a call.

6. The BSC informs the MSC when the traffic channel assignment is complete, and then the MSC/VLR starts to analyze the dialed number and sets up a connection to the called subscriber.

GSM System Survey

Traffic Cases

PSTN

Mobile Originated Call

BSC

MSC

PSTN

HLR

GMSC MSC

1

3

2

5

4

7

6

89

GSM System Survey

Mobile Terminating call

BSC

Traffic Cases

Roaming: Location Update

HLR

Attached

VLR ADD=Egypt Airport

Roaming & Int. Allowed

Detached


MSC/VLR

Is a roaming agreement present ?IMSI

60202..

Is r

oam

ing

an

d I

nt.

call

s al

low

ed ?

Attached

VLR ADD=Stock. Airport


Copy of the HLR Profile willbe stored in Stock. VLR

GSM System Survey

Traffic Cases

HLR

Attached

VLR ADD=xyz

GWMSC

MSC/VLR

Terminating Leg

Originating Leg

MSISDN

+2010….

GSM System Survey

Traffic Cases

Roaming: Call to HPLMN

HLR

Attached

VLR ADD=Stock. Airport

Roaming & Int. AllowedGWMSC

MSISDN

010…

MSC/VLR

Roaming Call Forwarding Leg

Originating Leg

GSM System Survey

Traffic Cases

Roaming: Call from HPLMN

HLR

GWMSC

MSC/VLRA

MSC/VLRB

Attached

VLR ADD=Stock. B


MSISDN

+2010….

Roaming CallForwarding Leg

Originating Leg

GSM System Survey

Traffic Cases

Roaming: Call from another Roamer

STCK.GWMSC

MSC/VLRA

MSC/VLRB

MSISDN+46…

GWMSCHLR

Terminating LegOriginating Leg STCK.HLR

GSM System Survey

Traffic Cases

Roaming: Call to The visited PLMN


GSM System Survey

Chapter 8 : GSM Services

What else other than voice?

Chapter Objectives


Know how do Fax and data calls take placeKnow how does SMS is sent and received Know how the call of a Prepaid subscriber takes place

GSM System Survey

GSM Services

Examples of GSM non-Speech services

Fax calls

Data calls

Short messages service (SMS)

Conclusion GSM is a telecommunication network rather than a telephony network.

GSM System Survey

GSM Services

Introduction

PSTN

What is the service requested ? e.g.. (speech, fax or data)

How will the service be performed ? E.g.. (bit rate)

Supported by :

The receiving node must know:

GSM System Survey

GSM Services

Fax and data Calls

ISDN GSM

Why do we have additional MSISDN for the same subscriber to be able to receive fax & data calls?

Information sent at call setup from ISDN or GSM on “how” the service will be performed, is called Bearer Capabilities (BC).

ISDN and GSM have different transmission requirements and different coding schemes, so they have different bearer capabilities referred to as ISDN-BC and GSM-BC.

PSTN can not provide this type of information during call setup, so it can not distinguish between a telephony call and a fax or data call.

An Additional MSISDN (AMSISDN) will be allocated to a mobile subscriber who has the service of receiving fax or data calls.

GSM System Survey

GSM Services

Fax and data Calls

For an MSC to be able to handle fax or data calls, it should be provided with a Data Transmission Interface (DTI) which is used for :

rate adaptation.

Protocol conversion.

such that Fax , Data calls are to be established to/from mobile subscribers.

Standard Bit Rate in GSM = 9.6 KB/SThis rate can be increased into 14.4 KB/S

The High Speed Circuit Switched Data (HSCSD) uses 4 time slots to perform a data call thus increasing the rate into 57.6 KB/S

Providing modems.

GSM System Survey

GSM Services

Fax and data Calls

AMSISDN IMSI

AMSISDN BCHLR

GWMSC MSC/VLR PSTN

AM

SIS

DN

AMSISDN

DTI

GSM System Survey

GSM Services

Fax and data Calls

Fax from PSTN

GSM fax call

MSC

DTI

PSTN

GSM System Survey

GSM Services

Fax and data Calls

GPRS General Packet Radio Services

( Up to 171 Kbit/sec)

EDGE Enhanced Data Rates for GSM Evolution

( Up to 48 Kbit/sec per channel)

UMTS Universal Mobile telecommunication System (Up to 2 MB)

GSM System Survey

GSM Services

Future Enhancements

Functionality& capabilities

Speech

Circuit data<9.6 kbps

HSCSD57.6 kbps

Circuit Switched

UMTS capable systems

GPRS115 kbps

Packet Switched

EDGE/IS-136384 kbps

WCDMA2 Mbps

1998 1999 2000 2001 20021997Time

High Speed Circuit Switching DataGeneral Packet Radio ServicesEnhanced Data Rate for GSM EvolutionWideband Code Division Multiple AccessUniversal Mobile Telecommunication System

GSM System Survey

GSM Services

GSM Evolution

The Short Message Service (SMS) allows a mobile subscriber to send and receive text messages composed of 160 characters at most.

The short messages sent or received are handled by the Short Message Service Center ( SMSC ), which consists of three parts :

Service Center (SC)

SMS GMSC (SMS-GMSC)

SMS inter-working MSC ( SMS-IWMSC)

GSM System Survey

GSM Services

Short Message Service

Service Center

Handles the delivery of short messages to/from Short Message Entities (SME), which can be any originator or receiver of short messages such as mobile, fax, … etc.

Stores the short messages. Create billing files. Monitors system events and alarms.

SMS-GMSC

Interrogates the HLR to determine the location of a mobile subscriber. Forwards the short message to a mobile subscriber via its serving MSC.

SMS-IWMSC

Receives the mobile originated short message from any MSC in the network.

Receives an alert message from the HLR to inform the SC that a mobile subscriber who was absent during a previous short message delivery attempt is reachable again.

GSM System Survey

GSM Services

Short Message Service

MO

MSC1 MSC2

MT

SMS - IWMSC SMS - GMSC

HLR

SC

Mobile Originated SMS

GSM System Survey

GSM Services

GSM System Survey

GSM Services

Unsuccessful Message Transfer

MO

MSC1 MSC2

MT


HLR

SC

Pending Message

Flag

Waiting Message

Data

GSM System Survey

GSM Services

The Mobile is present once more

MO

MSC1 MSC3

MT


HLR

SC

Alert: The MS is present

Alert :The MS is present



Attach

WAP Wireless Applications Protocol

CAMEL Customized Application of Mobile Enhanced Logic

GSM System Survey

GSM Services

Advanced GSM Services

MSCMSC IVRIVR

SDPSDP PPASPPAS

A pre-paid subscriber

858

IVR :Interactive Voice Recognition

PPAS:Prepayment Administration system.

SDP :Service Data Point.

868858 Charging

Balance inquiry 868

The Pre-payment system GSM System Survey

GSM Services

MSC 0MSC 0

SCP2SCP2

SCP3SCP3

SDP1SDP1

SDP2SDP2

A pre-paid subscriber

Pre-payment Originating call

MSC 13MSC 13 SDP1SDP1Oick-5

Oick-6

Oick-2

Oick-3

Oick-3Oick-6

Oick-2Oick-5

HLR

Oicksatellite

nodes

GSM System Survey

GSM Services


GSM System Survey

Thank You For your time

gsm system survey

Documents

o gsm mou

o gsm spec

o cept

areas o

o phase

finland o

o australia

bosch1998 o